In agricultural seed-drills with pneumatic distribution, there are conventionally used rotating distributors having blades which can be regulated in order to vary the quantity of material dispensed per unit of surface-area both via changes of speed and by means of volumetric variation of the bladed members of the distributor. The regulation brought about must be controlled by means of a so-called calibration operation before starting the distribution in the field so as to ascertain that the quantity of material effectively distributed per unit of surface-area corresponds to the desired expectations.
For that reason along the through-conduit for the material dispensed by the distributor towards the pneumatic transport device of the material, there is provided the possibility of varying the flow of the material being moved towards a collection container so as to be able to put into operation manually, in a simulated manner, the distributor and to weigh the material dispensed in that manner.
Typically, this operation is carried out by temporarily disassembling a portion of the distribution conduit.
This is really inconvenient because it requires that the operator slide between the tubes and components of the seed-drill until he reaches the gate or component to be disassembled, actuate the distributor, re-mount the component removed or move the gate and then come back out of the narrow position previously reached.
The inconvenience is such that very often the operator cannot check that the gate has been precisely replaced in the correct original position and starts the distribution of the product in the field with a calibration device which is open and not completely closed.
As an alternative to that solution, there are also known seed-drills which are provided with a gate which can be actuated in order to open or close an aperture in the conduit mentioned above and to obtain selectively a calibration position and a sowing position.
The Utility Model DE 10 2010 002200 describes a calibration device for seed-drills in which a conduit for transporting the sowing products is selectively opened or closed by means of a slidable member.
During the sowing step, the member is withdrawn from the conduit, thereby leaving it open and allowing the material to arrive at the seed distributors.
Conversely, in a second position, the member is introduced in the conduit and blocks the flow of material by means of a wall thereof, redirecting it towards a discharge aperture, thereby allowing the calibration step.
However, that solution also has disadvantages. Although there is provided the possibility of using actuators for activating the member, the use of a sliding linear member involves a specific risk of jamming of the device owing to dust, sand, straw and other material which is in the working environment and which may readily become introduced into the sliding members of the member.
In addition, when it is in a calibration position, the member intercepts the conduit in which the flow of air mixed with the product to be sown flows and during the movement of the member material, which may partially obstruct the conduit or the other sowing elements, can also readily be moved inside the conduit.